<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>css3云彩动画效果</title>
  <style>
    * {
      margin: 0;
      padding: 0;
    }

    .sky {
      position: relative;
      width: 100vw;
      height: 100vh;
      overflow: hidden;
      background-color: #007fd5;
      animation: sky_background 50s ease-out infinite;
    }

    .sky .clouds_one,
    .sky .clouds_two,
    .sky .clouds_three {
      position: absolute;
      top: 0;
      left: 0;
      width: 300%;
      height: 100%;
      transform: translate3d(0, 0, 0);
      animation: clouds_offset 50s linear infinite;
    }

    .sky .clouds_one {
      background: url(https://qiniu.zhangkai2019.cn/image/cloud_one.png) repeat-x bottom;
    }

    .sky .clouds_two {
      background: url(https://qiniu.zhangkai2019.cn/image/cloud_two.png) repeat-x bottom;
      animation-duration: 75s;
    }

    .sky .clouds_three {
      background: url(https://qiniu.zhangkai2019.cn/image/cloud_two.png) repeat-x bottom;
      animation-duration: 100s;
    }

    @keyframes sky_background {
      0% {
        background: #007fd5;
        color: #007fd5;
      }

      50% {
        background: #000;
        color: #a3d9ff;
      }

      100% {
        background: #007fd5;
        color: #007fd5;
      }
    }

    @keyframes clouds_one {
      form {
        left: 0;
      }

      to {
        left: -200%;
      }
    }

    @keyframes clouds_offset {
      form {
        left: 0;
      }

      to {
        left: -200%;
      }
    }
  </style>
</head>

<body>
  <div class="sky">
    <div class="clouds_one"></div>
    <div class="clouds_two"></div>
    <div class="clouds_three"></div>
  </div>
</body>

</html>